add Apertis model provider documentation

[Quert (theQuert)]

Summary

Add documentation for Apertis, a third-party model provider with OpenAI-compatible API that provides access to multiple LLMs.

Changes

• Create new provider page at providers/apertis.mdx
• Add Apertis card to all_providers.mdx
• Add Apertis accordion example to chat/index.mdx

Provider Details

• API Type: OpenAI-compatible (uses langchain-openai with custom base_url)
• Base URL: https://api.apertis.ai/v1
• Integrations: Chat, LLM, Embeddings
• Features: Tool calling, Structured output, Multimodal, Streaming

Test plan

• Verify provider page renders correctly at /oss/python/integrations/providers/apertis
• Verify Apertis card appears in All Providers list
• Verify Apertis accordion appears in Chat index page

[github-actions]

❌ Import check failed

This PR contains imports from langchain_core that should be imported from langchain instead.

Detailed issues

Analyzing diff for import issues...
 Found 4 import issues:

File: src/oss/python/integrations/providers/apertis.mdx
Line: 50
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage
Suggested: from langchain.messages import HumanMessage
--------------------------------------------------------------------------------
File: src/oss/python/integrations/providers/apertis.mdx
Line: 107
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage, ToolMessage
Suggested: from langchain.messages import HumanMessage, ToolMessage
--------------------------------------------------------------------------------
File: src/oss/python/integrations/providers/apertis.mdx
Line: 108
Issue: Import from langchain.tools instead of langchain_core.tools
Current:   from langchain_core.tools import tool
Suggested: from langchain.tools import tool
--------------------------------------------------------------------------------
File: src/oss/python/integrations/providers/apertis.mdx
Line: 147
Issue: Import from langchain.messages instead of langchain_core.messages
Current:   from langchain_core.messages import HumanMessage
Suggested: from langchain.messages import HumanMessage
--------------------------------------------------------------------------------

 Found 4 import issues that need to be fixed.

Why this is a problem

The langchain package re-exports many modules and classes from langchain_core. When possible, imports should use langchain instead of langchain_core for:

• Better user experience (single import source)
• Consistency across documentation
• Reduced cognitive load for users

How to fix

Replace the imports as suggested above. For example:

• ❌ from langchain_core.messages import HumanMessage
• ✅ from langchain.messages import HumanMessage

🤖 Automated check

This check is based on the latest analysis of langchain re-exports from langchain_core.

[Mason Daugherty (mdrxy)]

i think we'd prefer to remove this for now, as there are many nuances with regard to additions/abuses of the OpenAI spec to include non-unified/standard features

[Mason Daugherty (mdrxy)]

looks good after the requested change

[Quert (theQuert)]

Codex (@codex) review

[langchain-oss-automated-triage]

Thanks for contributing a new integration docs page, Quert (@theQuert)!

As of July 28, 2026, we have changed how we accept external integrations submissions. Please review the new integration submission process for more information.

We receive a large number of PRs and review them as quickly as we can. Please bear with us as we work through the queue.

If you have already tagged a maintainer on this PR, do not tag them again.

[Quert (theQuert)]

Codex (@codex) review

Latest head: 4746d8c (rebased onto current upstream main).

Resolved the provider-index conflict and narrowed the Apertis page to a catalog-neutral ChatOpenAI setup: the public model-list probe requires an API key (401), so the docs now direct users to their authenticated /v1/models result instead of claiming fixed model IDs or unsupported features.

Verified: uv run scripts/check_pr_imports.py, ruff format --diff, ruff check --diff, ty check, codespell src, and markdownlint for the provider page/index. No live model request was made because no API key was used.

[Naomi Pentrel (npentrel)]

Hi there, we've made a change to the effect that we no longer add external integration docs to our docs and instead link out to your docs directly from the overview table. I've made those changes here and will merge the PR once tests pass. Thanks!