New Integration Proposal: Synthorai

[cuihuan]

Summary and motivation

Requesting a new Haystack integration for Synthorai (https://synthorai.io), an OpenAI/Anthropic-compatible LLM gateway routing to 122 models across 11 upstream providers (Claude, GPT, Gemini, GLM, Kimi, DeepSeek, Qwen, etc.) at direct upstream pricing, no markup. Docs: https://synthorai.io/docs. Use case: one API key/base URL for both Claude-family and GPT-family models plus a longer tail of Chinese-origin models, without juggling multiple provider SDKs in a Haystack pipeline.

Adoption signals

Being upfront that Synthorai is early-stage, so these numbers are modest right now — flagging this as a heads-up request rather than expecting immediate prioritization, in case it's useful to have on record:

• GitHub stars: N/A (Synthorai itself isn't an open-source project; it's a hosted gateway)
• PyPI downloads: N/A, no Python SDK published yet — plain HTTP/OpenAI-SDK-compatible
• Release activity: Live production service, continuously updated
• Maintenance: Actively developed and maintained
• Haystack community demand: None yet that I'm aware of — this is a proactive request, not in response to existing community asks
• Anything else: Comparable integrations already exist for similar gateways (OpenRouter is already integrated at feat: Add OpenRouter integration #1723; Requesty's attempt at feat: add requesty-haystack integration #3581 was closed only for a missing CLA signature, not a rejection of the concept)

Detailed design

Following the OpenRouter integration (#1723) as a template: a new integrations/synthorai/ package with a SynthoraiChatGenerator wrapping the existing OpenAI-compatible generator machinery, defaulting api_base_url to https://synthorai.io/v1 and reading SYNTHORAI_API_KEY. Plain OpenAI-compatible surface, no custom request/response transformation needed.

I'm not attempting the PR myself yet given the adoption-signal bar described above — happy to if the team thinks it's worth building despite the early-stage numbers, and can use the scaffolding script per CONTRIBUTING.md at that point.

[cuihuan]

Belated but important disclosure: I'm affiliated with Synthorai — this request adds support for our own product, it isn't me reporting demand from elsewhere. I should have said so in the original post; flagging it now so the ask is judged on its merits with that context on the table.

No expectation of priority attached. Happy to do the implementation work myself, and equally happy to take "not now" for an answer.