Apex API — Terms for Individual Users

Effective from 1 October 2026

1. Who we are

The Apex API is provided by Callstack.io spółka z ograniczoną odpowiedzialnością, ul. Prosta 36, 53-508 Wrocław, Poland, entered in the Register of Entrepreneurs of the National Court Register kept by the District Court for Wrocław-Fabryczna in Wrocław, VI Commercial Division, under KRS number 0000606530, NIP 8992785616, REGON 363921820.

You can reach us at apex@callstack.com, or by post at the address above. For complaints, write to apex@callstack.com with "Reklamacja" in the subject line.

These Terms are also the terms of service (regulamin świadczenia usług drogą elektroniczną) required by Article 8 of the Act of 18 July 2002 on the provision of services by electronic means. You can read, download and save them at any time at https://apex.callstack.com/legal/individual-terms.

2. Who these Terms apply to

2.1. These Terms apply if you open an account as an individual — as a consumer, or as a sole trader entering a contract that is not of a professional character for you (przedsiębiorca na prawach konsumenta, Articles 7aa and 38a of the Consumer Rights Act and Articles 385⁵, 556⁴ and 556⁵ of the Civil Code).

2.2. If you are contracting on behalf of a company, or as a sole trader for purposes directly connected with your professional specialisation, the Commercial Terms at https://apex.callstack.com/legal/terms apply to you instead.

2.3. You must be at least 18 years old and have full legal capacity.

2.4. If the character of your use changes — for example, you begin using Apex in the course of a business you operate — tell us, and we will move your account to the Commercial Terms with effect from the date of the change. Rights you have already acquired are not affected.

3. What Apex is

3.1. Apex is a large language model that you access over an API. We built it by post-training a base model released by Qwen (Alibaba Group), which we use under licence, specialising it for React Native and React engineering. You send text and other data ("Input") and receive generated content ("Output"). Usage is measured in tokens and charged at the rates shown at apex.callstack.com/pricing.

3.2. The service consists of the API served at api.callstack.ai, the developer console at platform.callstack.ai, and the website at apex.callstack.com. We operate all of them.

3.3. To use the service you need an internet connection, an HTTPS client supporting TLS 1.2 or later, and a valid API key, which you create in the console. Supported endpoints, model versions, rate limits and interoperability information are set out in the documentation available in the console, which forms part of the description of the service. Your current rate limits are shown in the console.

3.4. Apex is a probabilistic system and its Outputs can be wrong. They may contain false statements presented confidently, may be incomplete or biased, and are not professional advice of any kind — legal, medical, financial or otherwise. Check anything you intend to rely on. Where an Output would affect someone's health, finances, legal position or safety, do not act on it without independent verification.

3.5. Outputs are not guaranteed to be unique. Another user sending similar Input may receive similar Output.

3.6. Apex was trained on open-source software, described in our Training Data Summary at https://apex.callstack.com/legal/training-data-summary. Its Outputs may occasionally reproduce or closely resemble code from that software. If you use such code in something you publish or distribute, check whether its licence requires you to include an attribution or notice.

4. Your account

4.1. Please give accurate registration details and keep them current.

4.2. Your API key works like a password. Keep it secret, do not publish it, do not embed it in an application you distribute, and do not share or sell it. You are responsible for usage incurred with your key. Tell us at security@callstack.com as soon as you suspect it has been exposed, and rotate it — you can do this yourself in the console at any time.

4.3. New individual accounts have a spending limit set by default. You can adjust it in the console. We recommend keeping a limit in place: an exposed key can generate charges quickly.

4.4. Please keep to one account per person. Do not create additional accounts to get around limits, credits or a suspension.

5. Prices and payment

5.1. Prices shown to you include VAT at the rate applying in your country of residence. The total amount payable is displayed before you confirm any purchase.

5.2. Payments are handled by Stripe Payments Europe, Limited. We are the seller; Stripe processes the payment. We do not see or store your full card number.

5.3. Credits. You buy credits in advance and use them as you make API calls. Credits can be used only to pay for Apex, are not transferable, and cannot be exchanged for cash. Credits do not expire.

5.4. Automatic top-up is switched off by default. If you switch it on, you authorise us to charge your saved card the amount you set, whenever your balance falls below the threshold you set. You can switch it off at any time in the console, with immediate effect.

5.5. We send a receipt or VAT invoice for every purchase by email, in a form you can save and print.

5.6. Price changes. We may change our prices for the future, giving you at least 30 days' notice by email. Credits you have already bought are not affected: usage is charged against them at the rates in force when you bought them. If you do not want to continue at the new prices, you can stop using the service and ask us to refund your unused balance.

6. Your right to withdraw within 14 days

6.1. You may withdraw from your contract with us within 14 days, without giving a reason. The period runs from the day the contract is concluded. Each purchase of credits concludes a separate contract and starts its own 14-day period.

6.2. To withdraw, simply tell us. You can use the withdrawal button in the console, email apex@callstack.com, write to our postal address, or use the model withdrawal form at the end of these Terms. Sending your message before the deadline is enough. We will confirm receipt by email straight away.

6.3. What happens to your money:

(a) If you asked us to start providing the service immediately — we ask you for this expressly at checkout — and you have used some of your credits, you pay for the usage you have actually consumed, calculated in proportion to the full scope of the contract. We refund the rest.

(b) If you have not used any credits, we refund the full amount.

(c) If you did not ask us to start immediately, we refund the full amount, including any usage.

6.4. We make refunds within 14 days of receiving your withdrawal notice, using the same payment method you used, unless you agree to a different method. Refunds cost you nothing.

6.5. This right is separate from, and in addition to, your rights if something is wrong with the service under Section 7. Withdrawing is not a complaint and you do not need to give a reason.

7. If something is wrong with the service

7.1. We must supply the service in conformity with the contract. This covers the description in these Terms, the documentation, and what you can reasonably expect from a service of this kind, including reasonable availability, security and continuity of supply. Your rights here come from Chapter 5b of the Consumer Rights Act and cannot be limited by these Terms.

7.2. If the service does not conform, tell us. You can require us to bring it into conformity. If we refuse, fail to do so within a reasonable time, or the problem recurs, you may require a reduction in price or withdraw from the contract, unless the non-conformity is immaterial.

7.3. Where we supply the service continuously, we are responsible for non-conformity arising at any time during the supply period, and it is for us to show that the service conformed.

7.4. We will tell you about updates, including security updates, that are necessary to keep the service in conformity, and will supply them for as long as we supply the service.

7.5. We do not exclude or limit our liability to you. We are liable for non-performance or improper performance of the contract under the general rules of Polish civil law. Nothing in these Terms restricts your statutory rights.

8. Changes to the service

8.1. We may change Apex — including retiring model versions, adjusting safety behaviour, and changing rate limits — where there is a valid reason, such as legal or regulatory requirements, security, capacity, or technical developments. Changes will not cost you anything extra.

8.2. If a change would materially and negatively affect your access to or use of the service, we will tell you at least 30 days beforehand by email, on a durable medium. You may then terminate free of charge within 30 days of the notice or of the change, whichever is later, and we will refund your unused balance. This does not apply if we give you continued access to the unchanged version at no extra cost.

8.3. We give at least six months' notice before retiring a generally available model version.

9. What you may not do

9.1. You must not use Apex for any of the following. These prohibitions admit of no exception.

(a) Child safety. Child sexual abuse material, sexualisation of minors, or any material facilitating the sexual exploitation of children.

(b) Weapons and mass harm. Developing or acquiring chemical, biological, radiological or nuclear weapons, or other means capable of causing mass casualties.

(c) Cyber harm. Creating malware, ransomware, exploits or denial-of-service tooling; gaining unauthorised access to systems; attacking critical infrastructure.

(d) Sexual and intimate-image harms. Non-consensual intimate imagery, or sexual content depicting real identifiable people without their consent.

(e) Fraud and deception. Fraud, phishing, identity theft, impersonation of real people or organisations, or spam at scale.

(f) Democratic process. Election interference, voter suppression, or fabricated statements attributed to real candidates or officials.

(g) Targeted harm to people. Harassment, stalking, doxxing, threats of violence, or incitement to violence or self-harm.

(h) Practices prohibited by Article 5 of the AI Act, including manipulative techniques causing significant harm, social scoring, untargeted scraping of facial images, emotion inference in workplaces or education, and biometric categorisation to infer protected characteristics.

(i) Attacks on the service. Reverse engineering the model, extracting its weights or parameters, using Outputs to train a competing model, or circumventing rate limits, safety filters, watermarks or provenance signals.

9.2. You must also not:

(a) submit other people's personal data without a lawful basis for doing so, or submit special categories of personal data within the meaning of Article 9 GDPR;

(b) resell API access to third parties;

(c) supply content of an unlawful character, as required by Article 8(3)(2)(b) of the Act on the provision of services by electronic means.

9.3. Some uses are allowed only with proper care. If you use Apex for legal, medical, mental-health or financial guidance, or in anything affecting someone's employment, education, credit, housing or immigration status, a person must review the Output before it is acted on, and you must tell affected people that AI is involved.

9.4. If you build something on Apex that other people use, you take on your own responsibilities for it. These include telling users they are dealing with an AI system where the law requires it, and any obligations you have under Regulation (EU) 2024/1689 (the AI Act) as a provider or deployer of an AI system. We are the provider of the Apex model; we are not responsible for what you build with it.

10. Your Input and Output

10.1. Whatever rights you have in your Input, you keep. You own the Output you generate, and we assign to you any rights in it that we might otherwise have.

10.2. You must have the right to submit whatever you submit.

10.3. We never use your Input or Output to train our models. The only content that can be used to improve Apex is feedback you deliberately send us — for example, a response you flag in the console.

10.4. Zero data retention. Your Input and Output are held in memory only while your response is being generated, and are then discarded. We do not write them to disk, logs or backups, and we cannot retrieve them afterwards — so keep your own copy of anything you need. We keep only the information needed for billing, rate limiting and security, such as timestamps, token counts and model identifiers.

10.5. Automated safety checks run on your Input and Output while they are being processed, to detect breaches of Section 9. They do not store your content.

10.6. We process your Input and Output within the European Economic Area.

10.7. How we handle your personal data is explained in our Privacy Policy at https://apex.callstack.com/legal/privacy.

11. Suspension and closing your account

11.1. You can close your account at any time in the console. We refund your unused credit balance within 14 days.

11.2. We may suspend or limit your access if you break these Terms, if the law requires it, if there is a security or fraud risk, or if your usage threatens the stability of the service. We will tell you why, unless we are legally prevented from doing so.

11.3. We normally give you a warning first, and limit or suspend access only if the problem continues. We may act immediately where the conduct falls under Section 9.1, where there is a risk of serious harm, or where the law requires it.

11.4. We restrict access no further than necessary, and restore it once the reason has been resolved. You can challenge any suspension under Section 12, and we will review it. If we terminate your account, we refund your unused balance unless the law prevents us from doing so.

11.5. We may close your account for other reasons on 60 days' notice, refunding your unused balance.

12. Complaints

12.1. Send complaints to apex@callstack.com with "Reklamacja" in the subject line, or in writing to our postal address. Please tell us what happened, when, and what you would like us to do.

12.2. We will respond within 14 days of receiving your complaint, on paper or another durable medium. If we do not respond within that time, your complaint is treated as accepted, in accordance with Article 7a of the Consumer Rights Act.

13. Out-of-court dispute resolution

13.1. If you are not satisfied with our response, out-of-court routes are available to you. In Poland these include the permanent consumer arbitration courts and the mediation conducted by the Trade Inspection (Inspekcja Handlowa), free assistance from your municipal or district consumer ombudsman (miejski lub powiatowy rzecznik konsumentów), and consumer organisations. The register of authorised bodies is maintained by the President of the Office of Competition and Consumer Protection (UOKiK) and is available at uokik.gov.pl.

13.2. If you live in another country in the European Economic Area, the European Consumer Centres Network (ECC-Net) can assist with cross-border disputes.

13.3. Callstack does not undertake in advance to participate in out-of-court dispute resolution, and will consider each request on its merits.

14. Changes to these Terms

14.1. We may change these Terms only where there is a valid reason: a change in the law, a decision of a court or regulator, a change in how the service works, the introduction of a new feature, a change in the terms on which our own suppliers charge us, or to correct errors and improve clarity.

14.2. We will email you at least 30 days before a change takes effect, and tell you what is changing.

14.3. If you do not accept a change, you may terminate before it takes effect, and we will refund your unused balance. Changes do not apply to anything that happened before they took effect.

15. Law and courts

15.1. Polish law applies to these Terms. This does not deprive you of the protection of any mandatory rule of the law of the country where you habitually reside, in accordance with Article 6 of the Rome I Regulation.

15.2. You may bring proceedings against us either in the Polish courts or in the courts of the country where you live. We may bring proceedings against you only in the courts of the country where you live.

Model withdrawal form

Complete and return this form only if you wish to withdraw from the contract. You are not obliged to use it.

To: Callstack.io sp. z o.o., ul. Prosta 36, 53-508 Wrocław, Poland — apex@callstack.com

I hereby give notice that I withdraw from my contract for the provision of the following service:

Ordered on: ......................................

Name: ......................................

Address: ......................................

Account email or customer ID: ......................................

Signature (only if this form is sent on paper): ......................................

Date: ......................................