docs(otel v2): presets export only to their own backend, add otel for a generic collector

[devin-ai-integration]

Summary

Companion to BerriAI/litellm#40881, which makes every OTel v2 preset (langfuse_otel, arize, arize_phoenix, weave_otel, newrelic, agentops, levo) export only to the backend it owns. Before that change a preset also inherited the operator's OTEL_* collector (or the stdout console placeholder), so vendor vocabulary such as langfuse.* or OpenInference landed on the generic collector

The "Send to several backends at once" tip now says that a preset ignores OTEL_* on its own, and shows callbacks: ["otel", "langfuse_otel"] as the way to get plain gen_ai.* spans on your own collector next to a vendor preset

Link to Devin session: https://app.devin.ai/sessions/ef5e75844495467e92662e55750e1dd1
Open in Devin Desktop: https://app.devin.ai/desktop/session/ef5e75844495467e92662e55750e1dd1?variant=devin
Requested by: @yucheng-berri

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment, CI, and merge conflict monitoring

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated
litellm	Ready	Preview	Sep 12, 2026 11:52pm UTC