How Synthetic works

Synthetic is a subscription service that runs open-source coding LLMs on dedicated infrastructure and serves them over an OpenAI-compatible (and Anthropic-compatible) API. Instead of paying per-token, you pay a flat monthly subscription and get a generous rate-limit budget covering every model on the platform.

It’s positioned as a direct alternative to Claude’s $20/month and $200/month plans for developers who do a lot of coding: the same price point, several-times-higher rate limits, and your choice of open-source models.

Mesrai reaches Synthetic through the OpenAI-compatible endpoint, so there are no adapter changes — just BYOK credentials.

Plans at a glance

Subscription (recommended for code review)

• All standard models are covered by the subscription — pick any of them by changing the model field.
• Rate limits are enforced on a 5-hour rolling window, not per month — plan concurrency to fit inside that window.
• Synthetic does not train on your prompts/completions and deletes API data within 14 days.

Recommended models

Synthetic exposes models using a HuggingFace-style prefix (hf:org/model). A few strong picks for code review:

See the full catalog at dev.synthetic.new/docs/openai/models.

Creating an API Key

1. Go to synthetic.new and sign up or log in.
2. Subscribe to a plan at synthetic.new/pricing.
3. Open the developer console and create an API key. Copy it immediately — you will not see the full key again.

Configure Synthetic in Mesrai

The primary flow is BYOK on Mesrai Cloud. Self-hosted installs can use environment variables as a secondary option.

Option 1 — BYOK on Mesrai Cloud (recommended)

1. In the Mesrai web UI, open Settings → BYOK (app.mesrai.com/organization/byok).

2. Synthetic isn’t in the curated catalog — click Configure manually at the bottom of the model list. Use ?slot=fallback in the URL if configuring a fallback instead of the main model.

3. Fill the wizard:

   Field	Value
   Provider	OpenAI Compatible
   Base URL	https://api.synthetic.new/openai/v1
   Model	e.g. hf:zai-org/GLM-4.6 (use the hf: prefix and the full HuggingFace path)
   API Key	your Synthetic API key
   Max Concurrent Requests	start at 3–5 to fit the 5-hour budget on bigger PRs (under Advanced settings)

4. Click Test & save. Mesrai probes the endpoint and persists the config on success. 401 means the key is wrong; 404 usually means the base URL or model path is wrong.

Enterprise deployments

For Enterprise customers running Mesrai in their own VPC, the Synthetic block is configured via environment variables in the API + worker containers. Your onboarding contact will share the exact .env template and deployment runbook for your tenancy. Contact sales for details.

When to pick Synthetic

• Your primary model is open-source (Kimi, DeepSeek, Qwen Coder, GLM) and you want a single flat-rate bill instead of juggling per-provider token spend.
• You’re comparing to Claude Max ($200/mo) for review throughput — Synthetic at $30/mo delivers several times the rate-limit budget for similarly-capable coding models.
• You want strong data posture — Synthetic is explicit about no-training and 14-day prompt/completion retention.

Pick pay-per-token (Moonshot, Fireworks, Together, Groq) instead if traffic is bursty, or a different subscription (Z.AI GLM Coding Plan) if you specifically want the GLM family with tiered commits.

Troubleshooting

Related

• Synthetic pricing
• Synthetic API docs
• Synthetic model catalog
• BYOK overview