Streamline LLM Gateway quickstart: tabbed SDK examples - #5981

The model_provider='openai' + model='anthropic/claude-opus-5' combination
was confusing. Replace with a single clean example using the langsmith:
provider prefix and LANGSMITH_GATEWAY=true, which is unambiguous and
requires no explanation of the OpenAI-compat forwarding internals.

…y notes

- Rename LANGSMITH_GATEWAY_BASE_URL to GATEWAY_URL in shell examples with
  a comment clarifying it is a local shell variable, not one the SDKs read
- Add two-sentence intro before the tabs explaining the two flows:
  unified /v1 endpoint (cURL, OpenAI/Anthropic SDKs) vs LANGSMITH_GATEWAY
  env var (LangChain, Deep Agents)
- Add Warning: do not append /v1 path to LANGSMITH_GATEWAY value; SDK
  appends provider path automatically — doubled path causes failures
- Add comment in Anthropic SDK tabs: gateway root has no /v1 suffix
- Add Note: only chat models route through LANGSMITH_GATEWAY; embeddings
  and legacy LLM integrations are unaffected
- Add Note: 403 at call time (not setup time) indicates missing
  gateway:invoke permission
- Add Note to TypeScript accordion flagging rows that may diverge from
  Python implementation; recommend verifying against @langchain/openai

Gateway Credits are only for moonshotai/kimi models on Fireworks — they
are not a general alternative for BYOK models. Remove the incorrect
suggestion that langsmith: prefix = Gateway Credits access, and remove
the 'You can call a Gateway Credits model without a provider secret'
intro sentence. Replace with a single link to the credits page in the
how-the-gateway-works step. The quickstart now stays focused on
BYOK usage.

- Drop 'two ways to reach the gateway' block before tabs — context is
  now inline in each tab as prose above the code block
- Remove 'Pick the tab that matches your SDK' line
- Move code comments on GATEWAY_URL into prose lines above code blocks
- Rename 'LANGSMITH_GATEWAY env var (LangChain and Deep Agents)' to
  'Using LANGSMITH_GATEWAY'

The two tables had identical rows — only column names (OPENAI_API_BASE
vs OPENAI_BASE_URL, base_url= kwarg vs configuration.baseURL) and 3
'Resolved key' cells differed between Python and TypeScript. Replace
the two accordions with one that:
- Lists supported models for Python and TypeScript separately
- Uses a single merged table with generic column headers
- Marks the 3 diverging rows inline with a dagger (†) footnote

…to tabs

- Add 'Gateway URLs' section with US / EU / BYOC base URLs in a table,
  plus a two-bullet explanation of unified /v1 vs direct provider routes
  with links to the relevant reference pages
- Remove separate 'Set your API key' step; fold LANGSMITH_API_KEY export
  into each tab's setup block alongside LANGSMITH_GATEWAY where relevant,
  so all env vars are visible in context
- Inline regional URL comments in GATEWAY_URL definitions and
  LANGSMITH_GATEWAY examples (US default / EU / BYOC on commented lines)
- Remove numbered steps from 'Make a call', 'View your trace', and
  'Set a spend policy' since step 1 is gone

- Remove 'Gateway URLs' section from near the top
- Strip regional URL comments from all inline code examples
- Add 'Regional URLs and endpoint styles' section before Next steps,
  covering US/EU/BYOC base URLs and the unified /v1 vs direct provider
  route distinction

- Remove intro sentence 'Set your API key...'
- Replace flat SDK tabs with format-based outer tabs:
  Chat completions / Messages / Responses / Deep Agents / LangChain
- Each tab uses <CodeGroup> for language switching (cURL, Python, TypeScript)
  matching the pattern used in llm-gateway-api-formats.mdx
- Use consistent prompt 'Explain what an LLM gateway does in one sentence.'
  across all examples
- Messages tab: add Anthropic-Version header to cURL example
- Responses tab: use client.responses.create per reference snippets

Four pages linked to anchors that no longer exist after the quickstart
was restructured:
- #2-make-a-call → #make-a-call (step numbering removed)
- #using-langchain-and-deep-agents → #using-langsmith_gateway (section renamed)

…ateway-quickstart

- Prerequisites: tighten 'To set this up, see' -> 'See'; cut 403 Note
  (covered by the permissions bullet; troubleshooting not a prereq)
- Tab intros: 'Works with' -> 'Use this with' (active, task-first)
- Deep Agents Python: remove unused 'import os'
- View your trace: 'navigate to' -> 'go to'; cut trailing Note about
  separate gateway/app traces (edge case, not quickstart material)
- Set a spend policy: tighten closing line to single link
- Automatic routing Warning: 'will cause' (future tense) -> 'causes'
- Collapse two Notes into one (chat-models-only + LANGSMITH_GATEWAY_API_KEY)
- Regional URLs: remove redundant 'When you set LANGSMITH_GATEWAY...' sentence;
  tighten endpoint bullet descriptions
- Accordion footnote: shorten

- Rename 'LangChain / per-request' tab to 'LangChain'
- Show LANGSMITH_GATEWAY=true pattern (consistent with Deep Agents tab)
  instead of the langsmith: prefix as the main example
- Remove the Deep Agents code block from the LangChain tab
- Add a <Tip> explaining the langsmith: per-model prefix as an
  alternative to the global LANGSMITH_GATEWAY setting; notes it
  works with both init_chat_model and create_deep_agent
- Fix double-comment formatting: split into two separate comment lines
  in both Deep Agents Python and TypeScript blocks

- Remove LangChain tab (keep Deep Agents, Chat completions, Messages, Responses)
- Move langsmith: per-agent tip into Deep Agents tab as a <Tip> block,
  showing create_deep_agent(model='langsmith:anthropic/claude-opus-5')
  and explaining LANGSMITH_GATEWAY is global vs per-agent via langsmith: prefix
- Fix Deep Agents comment formatting: each export on its own comment line
- Add LANGSMITH_API_KEY (first) to the Automatic routing code block
- Endpoint styles: unified /v1 is recommended and translates between API
  formats; direct provider routes pass through without format translation

- Remove <Accordion> wrapper — content is now always visible
- Rename to 'Supported LangChain integrations' heading (h3 under section)
- Collapse Python/TypeScript package bullet lists into a single table
  with Provider, Python package, TypeScript package columns
- Replace 12-row truth table with simple ordered precedence rules:
  Base URL (4 rules) and API key (3 rules), first match wins
- Fix Warning: now shown after the URL form of LANGSMITH_GATEWAY is
  introduced (commented lines), so the 'no path suffix' instruction
  makes sense in context
- Add commented EU/BYOC URL variants to the env var block so the
  Warning's mention of URL values is no longer a surprise
- Collapse TypeScript divergence note to one sentence at the bottom

… URLs

- 'Automatic routing (LangChain and Deep Agents)' → 'Using LangChain SDKs'
- Split two-point Note into two separate Notes (chat models / LANGSMITH_GATEWAY_API_KEY)
- Replace 7-rule precedence list with a 3-row override table + 1 sentence
  for key resolution — much faster to scan
- 'Regional URLs and endpoint styles' → 'Gateway URLs' with two h3
  subsections: 'Regional instances' and 'Unified endpoint vs direct
  provider routes'; bold the key distinction (translates vs does not)
- Fix cross-reference in manage-prompts-programmatically.mdx to new anchor

Replace abstract bullet points with a table using the concrete base URL
from the regional instances section, showing the full URL for each
endpoint style (unified /v1/chat/completions, /v1/messages, /v1/responses,
and direct provider route with no suffix). Keeps format translation
distinction bolded.

- 'lowest-priority routing signal' -> 'More specific settings take priority over'
- Remove em-dashes from table cells; 'Yes — always' -> 'Yes, always'
- '— (this is the gateway setting)' -> 'This is the gateway setting'
- 'takes precedence over' -> 'takes priority over'
- 'when the gateway URL is in use' -> 'when the gateway is in use'
- 'unexpected routing' -> 'unexpected behavior'

- Tighten opening sentence; move 'no per-client wiring' to second clause
- Remove bold on 'chat model' (redundant with the Note below)
- Warning: shorten 'a doubled path and request failures' -> 'doubles the
  path and causes failures'
- Merge two Notes into one (chat-models-only + LANGSMITH_GATEWAY_API_KEY)
- Override table: rename 'Overrides gateway?' column to 'Priority';
  use Highest/Higher/Base instead of Yes/Yes/'This is the gateway setting'
- Remove TypeScript edge-case Note (vague; better to just test)

- Override precedence: replace two-column table with a numbered list
  (1 = highest priority, 3 = base) — self-evident without a column header
- Add parallel numbered-list sentence for API key precedence
- Move LANGSMITH_GATEWAY_API_KEY guidance out of Note bubble into plain prose
- Opening sentence: 'no per-client base_url or api_key wiring needed' ->
  'Each integration picks up the gateway automatically from the environment'

- Collapse 3 unified /v1 rows into one: URL is /v1, description explains
  it accepts all 3 formats and translates between them
- Direct provider route: add concrete Anthropic example showing the full
  URL the SDK hits, so readers understand what 'SDK appends its own path' means
- Rename 'Style' column to 'Endpoint'

Anthropic's model overview lists Claude Sonnet 4.6 under legacy models.
The current lineup is Fable 5.1, Opus 5, Sonnet 5, and Haiku 4.5, and
Anthropic recommends starting with Opus 5 for most workloads.

Scoped to the two pages this branch adds. The rest of the gateway set
still carries claude-sonnet-4-6.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Anthropic lists Claude Sonnet 4.6 under legacy models. Updates the
remaining 16 illustrative references across the gateway set so the
examples agree with the quickstart.

All 16 are illustrative model IDs, not deliberate references to an
older model. The models-list response on the API formats page already
used claude-opus-5, so no duplicate entry is introduced.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

The tabs explained what each one does but not how to choose between
them. Adds two sentences inside the first step: what a gateway call is,
then when to reach for Chat completions versus Deep Agents.

Step titles left as short imperative phrases, matching the ~512 other
<Step title> values in the corpus.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Matches the 12 sibling gateway pages that put the note directly after
the frontmatter. The previous placement followed llm-gateway-api-formats,
which is the one page in the set that does it the other way.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

The note was duplicated inline on 16 pages, so the wording will need 16
edits when the gateway reaches GA. Extracts it to
snippets/langsmith/llm-gateway-beta-note.mdx and imports it everywhere,
following the Managed Deep Agents pattern.

Also:
- Adds the note to llm-gateway-monitoring.mdx, the one page in the set
  that was missing it.
- Drops the redundant "**Beta:**" prefix; the note now reads "The LLM
  Gateway is in beta."
- Normalizes placement on llm-gateway-api-formats.mdx, which had the
  note below the intro.
- Removes the page-level `tag: "Beta"` frontmatter added earlier, since
  no other page in the set uses it and the nav item already carries one.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Three hand-authored miscasings of the product name. Capitalization only,
so the #use-with-the-langsmith-gateway heading anchor is unchanged and
its inbound link still resolves.

Leaves alone the uses that are correctly lowercase: "an LLM gateway" as
a generic category noun (the auth-proxy page, third-party provider
listings, the quickstart's own example prompt) and the Kubernetes
Gateway resource on the self-hosted pages.

Does not touch changelog.mdx or self-hosted-changelog.mdx, which carry
36 more instances. Both are generated (changelog-weekly from
langchainplus fragments, self-hosted by the helm bot) and published to
RSS, so the fix belongs upstream in the fragment source.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>