docs(tag-routing): add negation tags and tag_regex sections

[deepanshululla]

Relevant issues

Companion to litellm OSS PR #31680 (tag routing negation feature).

Changes

• Rewrites docs/proxy/tag_routing.md to incorporate existing page content (Quick Start, Calling via Request Header, Setting Default Tags, Team based tag routing) with improved formatting
• Adds Negation Tags (Denylist) section: !-prefix tags to exclude deployments by tag, with examples for single provider, multiple providers, fallback chains, and header-based usage
• Adds Regex-based tag routing (tag_regex) section: operator-configured regex matching against User-Agent, with config example, verification steps, observability output, and a security caution note clarifying that header-based routing is not a security boundary and requires an upstream auth layer

Type

📖 Documentation

---

Note

Low Risk
Documentation-only changes to proxy tag routing; no runtime code or config behavior is modified in this PR.

Overview
docs/proxy/tag_routing.md is reworked to keep the existing quick start, header tags, default tags, and enterprise team routing, with cleaner Docusaurus-style examples (showLineNumbers, bash/json fences) and a shorter quick-start flow.

The main new material documents negation (denylist) tags (!tag in request metadata.tags or x-litellm-tags): how to exclude deployments by exact tag, combine with positive tags, handle ban-only requests, fallbacks, failure mode no_deployments_with_tag_routing, and a semantics table (no regex on client negation tags, untagged deployments never excluded).

It also adds/expands tag_regex operator routing on User-Agent, including matching semantics, observability payload, caution that header routing is classification not access control, and how negation runs before regex (with two interaction examples).

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Project	Deployment	Actions	Updated (UTC)
litellm	Ready	Preview, Comment	Jun 30, 2026 4:42am

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