Why Windsurf and Codeium Need Their Own Clash Story (Not a Cursor Rerun)

In 2026, the AI coding landscape is crowded: assistants ship inside IDEs, fetch models from multiple clouds, and mix web sign-in, long-lived API sessions, and occasional large binary or plugin delivery paths. Windsurf Editor, built on the Codeium platform, is a distinct client from Cursor IDE. The hostnames you must route are different, the failure signature is different (often “blank Cascade” or endless loading rather than a single marketplace CDN), and the fix is different from bolting a few OpenAI lines into a catch-all PROXY bucket.

This page stays in the developer proxy genre: you already run Clash (or a Mihomo-family core) for daily work, and you want split rules that are explicit enough to debug. It complements our Cursor-focused walkthrough, which dissects *.cursor.sh APIs versus VS Code-style marketplace and CDN traffic. If you need that parallel, read the Cursor split-rules guide after you understand the pattern here; the two articles intentionally do not share the same hostname inventory.

At a high level, success means three things: the rule engine actually sees the DNS names your app resolves, your rules list evaluates vendor hosts before a noisy GEOIP shortcut, and you verify each hop with connection logs instead of guesswork. API timeout symptoms in Electron apps are often indistinguishable from a wrong node until you look at which domain lost first.

Typical Symptoms: The Shell Loads, the Cloud Brain Does Not

Network tickets from Windsurf and Codeium users on restrictive or split networks tend to cluster around a few user-visible states. The editor window renders; local files open; Git and terminals may work. Then Cascade or inline assistance shows a blank panel, a perpetual spinner, or a generic “Failed to connect” class of error. Inline completions stutter or never arrive. Sign-in to the Codeium or Windsurf account flow fails in ways that a normal browser session on the same machine does not replicate.

That asymmetry is the giveaway. If Chrome reaches SaaS UIs but the IDE does not, you are not debugging “the internet”; you are debugging which TLS flows the IDE generates, which Strategy group (policy group) they hit in Clash, and whether a domestic-direct rule stole half the session. The Codeium team documents that corporate filters should whitelist specific domain families; when your problem is a personal Clash policy instead of a corporate firewall, you translate the same idea into DOMAIN-SUFFIX rows and ordered rules.

Another frequent confusion is conflating rate limits with routing. Codeium and Windsurf can show capacity-related errors when their backends are hot; that is not something Clash fixes. Still verify routing first: a mis-socketed API path can look like a model stall when it is really a three-way split where *.codeium.com and *.codeiumdata.com took different outbounds, leaving one long poll half-open on a path that your resolver never matched cleanly.

Official Domain Families You Should Map First

According to the public Windsurf troubleshooting documentation for network filters, firewalls, VPNs, and proxies, you should allow the following pattern families: *.codeium.com, *.windsurf.com, and *.codeiumdata.com. Treat that trio as the minimum roster for a serious profile. Product teams can add or rotate shards, so your operational habit should always be: start from the vendor list, then refine with the hostnames you actually observe in the Clash connection log after one representative session.

Within codeiumdata.com, you may see hostnames that carry plugin or distribution payloads—examples discussed in the ecosystem include windsurf-stable.codeiumdata.com for certain download paths. The precise labels move faster than a blog can freeze them, which is another reason to prefer DOMAIN-SUFFIX over a dozen brittle DOMAIN lines that rot after every client update. Reserve single-host DOMAIN rules for buckets you have proven in logs to need isolation from their siblings.

Also remember what this list is not. It is not a catalog of every third-party model or search integration you may enable in the future. If you connect optional tools that call another vendor (for example a web search or retrieval API with its own api.* host), you must add or merge those suffixes in the same first-match spirit. A profile that is perfect for base Windsurf and still drops optional features is not wrong; it is incomplete. Layer those extras only after the Codeium-first path is green.

Designing Policy Groups: One Lane or Split AI versus Payloads

Two configurations cover most people. The simpler design introduces one select or url-test Strategy group—name it CODEIUM or WINDSURF for clarity—and points all three official suffixes at that group. The finer design splits CODEIUM_API (interactive model calls, long streams, auth surfaces under codeium.com and windsurf.com) from CODEIUM_DATA (large, bursty, or update-style fetches on codeiumdata.com when logs show a benefit). The split helps when the best node for low-latency chat is not the best for a fat artifact download, or when a carrier shapes one path but not the other.

Whatever you pick, the YAML must reference proxy-groups entries that really exist. Snippets copied from public forums often mention emoji-labeled outbounds; if your file never defined that label, Clash will not invent it. When you are learning, it is fine to let CODEIUM mirror membership from your main PROXY group so behavior matches what already works in the browser, then narrow once logs justify specialization.

Latency and health checks still matter. Streaming completions and agent loops keep sessions warm; a borderline node that looks “green” in a ping list can still be wrong for an HTTP/2-heavy workload. Configure url-test with realistic intervals; avoid flapping test URLs that make Clash look alive while the upstream silently buffers. The foundational story for ordering GEOIP and MATCH lives in the rule-based routing explainer—read it once if you are new, then return here for vendor-specific lines.

A Concrete Rule Block (Illustrative YAML)

The following excerpt is intentionally conservative. Place these lines above any broad GEOIP or regional direct rules so first-match semantics do not send Codeium traffic down the wrong default. Rename outbounds to match your profile; verify suffixes against your log after a real Windsurf session.

# Illustrative only — confirm suffixes in your connection log
proxy-groups:
  - name: CODEIUM_API
    type: select
    proxies:
      - NODE-A
      - NODE-B
      - DIRECT
  - name: CODEIUM_DATA
    type: select
    proxies:
      - NODE-B
      - NODE-A
      - DIRECT
  # If you prefer one bucket, use a single CODEIUM group and
  # point all three DOMAIN-SUFFIX lines to it.

rules:
  - DOMAIN-SUFFIX,codeium.com,CODEIUM_API
  - DOMAIN-SUFFIX,windsurf.com,CODEIUM_API
  - DOMAIN-SUFFIX,codeiumdata.com,CODEIUM_DATA
  # If collapsed to one group, replace CODEIUM_API/DATA with CODEIUM
  # ... your GEOIP / MATCH follow ...

The critical discipline is that nothing in the Windsurf or Codeium stack is served exclusively from a single country-shaped bucket. A premature GEOIP,US,DIRECT-style line can win before your DOMAIN-SUFFIX if you put it first. The entire history of “Clash is fine except my AI IDE” threads lives in that ordering mistake.

Rule Order, Shared CDNs, and the GEOIP Footgun

First match wins, but humans reason about last intent. The mental model is simple: anything that is specific to AI coding vendors should appear before any shortcut that classifies “the rest” of the world by country. Fuzzy GEOIP rules are great until they mis-tag an anycast edge that your vendor shares with a completely unrelated SaaS. When the symptom is intermittent stalls rather than hard failures, the bug is very often a partial match: some flows hit the right Strategy group, some do not.

Be cautious about reusing wide infrastructure rules. A line that matches a huge cloud storage suffix might be correct for a log-derived bucket you truly need, but it can also drag unrelated development traffic. Prefer measured additions from your own logs. When two community rule sets both define the same suffix with different outbounds, first match wins and second source silently does nothing; merge deliberately.

If you enable optional integrations that are not in the default three-suffix set, add them in the same section so they are not left under a catch-all you intended for “short web browsing” only. The difference between a tool that “sort of works” and one that is production-stable is usually completeness of the allow path, not cleverness of the node list.

DNS, Fake-IP, and Why Electron Ignores “The System Proxy”

Clash is not clairvoyant. DNS mode, fake-ip, and OS-level DoH or Private DNS can each change the names the rule engine observes. A classic failure mode: the browser used Clash DNS, the IDE used an encrypted resolver, and your DOMAIN rows never saw the right strings. The fix is to align the resolver path your IDE uses with the one your profile assumes, or to enable transparent capture so the traffic cannot quietly bypass policy.

Many Electron-based editors do not use the system HTTP proxy the same way a browser does. Windsurf can detect proxies when configured, but your Clash stack still needs a coherent view of the flow. If you rely on TUN to capture reluctant apps, use the TUN mode guide for mode-specific gotchas, then re-test. If you are still in pure system-proxy mode, read the system proxy versus TUN article to understand which processes voluntarily participate and which do not.

HTTP/2 and long-lived streams add another wrinkle. Some middleboxes and cheap nodes make streaming look like a hang. When domain routing is already correct, still consider upstream quality: split rules remove an entire class of self-inflicted pain, but they cannot fix an overloaded exit or aggressive TLS inspection you do not control.

Windsurf Proxy Settings: What the App Expects

The official Windsurf documentation explains proxy behavior inside the app: a “Detect proxy” path that reuses the system or PAC-based configuration, manual proxy URL and credentials, and separate remote-SSH or dev-container proxy fields when you work on a remote host. If your Clash plan assumes the desktop should pick up a system proxy, that detection path is where configuration meets reality. If your environment is cleaner with explicit TUN, you may not need the UI fields at all—still worth knowing they exist, because a half-configured remote session can make Cascade look “online locally” but broken in the container.

Treat the documentation as a companion to this routing guide, not a substitute. Firewalls whitelists talk about domains; Clash needs ordered rules and consistent DNS. When both align, the IDE stops being a special case that only works when you disable your proxy “to test something quickly.”

How to Verify Without Random Node Swaps

Adopt a boring ritual. After every policy change, open Windsurf, sign in if needed, open Cascade, and request a small inline completion. Watch the Clash log for the hostnames you expect from the three official suffixes. If you see a surprise domain, add it deliberately rather than papering over with FINAL,PROXY and calling it a day.

Second, trigger a path that uses codeiumdata.com if your session does—updates, stable-channel payloads, or similar—and confirm the outbound. Third, if you use remote development, exercise the remote once and compare logs between local and remote failures. Mismatches there often point to the separate remote proxy fields rather than the desktop rule file.

When logs are too noisy, filter by codeium and windsurf substrings. Keep a one-line note in your private docs of the working stack: app version, Clash core, DNS mode, group names, and whether TUN is on. Future updates will change hostnames; your future self will only care about the diff.

How This Pairs With MCP and Cursor Articles on This Site

We publish toolchain-oriented split guides for adjacent problems. The MCP-focused article attacks Model Context Protocol traffic and registries, which is a different problem from Codeium’s first-party host families. The Cursor article handles *.cursor.sh and marketplace-adjacent paths. None of these pages should be mixed blindly: copy host lists only after you have confirmed overlap in your own logs, not because both IDEs are “AI editors.”

What Split Rules Cannot Fix

Clash can route packets; it cannot fix expired subscriptions, vendor outages, or account-level limits. It also cannot override employer security or local law. If your organization forbids exfiltration to certain regions, a technical path that works on your lab machine may still be non-compliant. Treat routing as a hygiene layer on networks you are allowed to shape.

Closing Thoughts

In 2026, a stable AI programming stack on the desktop is as much a routing problem as a model problem. Clash split rules for Codeium and Windsurf are not magic: they are a faithful translation of the vendor allowlist into first-match DOMAIN-SUFFIX rows, aligned DNS, and a verification loop that treats the connection log as ground truth. Compared with ad hoc “turn everything global” testing, a narrow policy keeps latency understandable and failures reproducible—exactly what you want when a deadline looms and Cascade is still spinning.

If you are comparing profiles across your tooling, pair this file with the Cursor guide only for methodology, not for copy-pasting hostnames. The competitive landscape between AI IDEs is loud; your Clash file should stay boring and correct.

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