diff --git a/bin/ultracode b/bin/ultracode
index 858445d..dc83190 100755
--- a/bin/ultracode
+++ b/bin/ultracode
@@ -52,11 +52,37 @@ PORT="${UC_LISTEN_PORT:-$("$PY" -c 'import json,sys;c=json.load(open(sys.argv[1]
 UPSTREAM="${UC_UPSTREAM:-$("$PY" -c 'import json,sys;c=json.load(open(sys.argv[1]));print((c.get("proxy") or {}).get("anthropic_upstream") or "https://api.anthropic.com")' "$CONFIG" 2>/dev/null || echo https://api.anthropic.com)}"
 BASE_URL="http://127.0.0.1:${PORT}"
 
+# 1M context window enablement ------------------------------------------------
+# Claude Code only switches its context meter AND auto-compaction to the 1M
+# window (and sends the context-1m beta) when the model id carries the [1m]
+# suffix. The selector and config advertise bare ids (e.g. claude-opus-4-8), so
+# without this the client sizes context at 200k -- the meter fills ~5x too fast
+# and pins at 100% -- even though Opus 4.8 / Sonnet 4.6 serve 1M natively. We
+# append [1m] to 1M-capable Claude base ids before launch. Disable with
+# UC_FORCE_1M=0; override the capable set with UC_1M_MODELS (comma-separated).
+UC_FORCE_1M="${UC_FORCE_1M:-1}"
+UC_1M_MODELS="${UC_1M_MODELS:-claude-opus-4-8,claude-opus-4-7,claude-opus-4-6,claude-sonnet-4-6}"
+uc_add_1m() {
+  # Echo $1 with a [1m] suffix iff it is a bare, 1M-capable Claude id. Anything
+  # else (Auto Router, Gemini/GPT/Composer, Haiku, already-suffixed, empty) is
+  # passed through untouched.
+  local m="$1" id
+  if [[ "$UC_FORCE_1M" == "0" || -z "$m" || "$m" == *"[1m]"* ]]; then
+    printf '%s' "$m"; return
+  fi
+  IFS=',' read -ra _uc_1m_ids <<< "$UC_1M_MODELS"
+  for id in "${_uc_1m_ids[@]}"; do
+    if [[ "$m" == "$id" ]]; then printf '%s[1m]' "$m"; return; fi
+  done
+  printf '%s' "$m"
+}
+DEFAULT_MODEL="$(uc_add_1m "claude-opus-4-8")"
+
 # Session settings (ultracode + discovery env).
 cat > "$SETTINGS" <<JSON
 {
   "ultracode": true,
-  "model": "claude-opus-4-8",
+  "model": "$DEFAULT_MODEL",
   "env": {
     "ANTHROPIC_BASE_URL": "$BASE_URL",
     "CLAUDE_CODE_WORKFLOWS": "1",
@@ -160,6 +186,10 @@ if [[ "${UC_SELECTOR:-1}" != "0" && -f "$SELECTOR" ]]; then
     echo "Selector unavailable; launching with default model."
     SELECTED_MODEL=""
   fi
+  # Upgrade a 1M-capable Claude pick to its [1m] variant so the client uses the
+  # full 1M context window (meter + auto-compaction), not the 200k default.
+  SELECTED_MODEL="$(uc_add_1m "$SELECTED_MODEL")"
+  [[ -n "$SELECTED_MODEL" ]] && echo "Orchestrator model id: $SELECTED_MODEL"
 fi
 
 HAS_MODEL_ARG=0
diff --git a/docs/TROUBLESHOOTING.md b/docs/TROUBLESHOOTING.md
index 4a6137e..aa30e54 100644
--- a/docs/TROUBLESHOOTING.md
+++ b/docs/TROUBLESHOOTING.md
@@ -262,6 +262,34 @@ side — here, all on Windows). The cleanest way to make any model follow the ru
 above automatically is to drop them into a `CLAUDE.md` (project root, or the global
 `~/.claude/CLAUDE.md`).
 
+### Context fills up too fast / `/context` shows `200k` for a 1M model
+
+**Symptom.** You picked Opus 4.8 (or Sonnet 4.6) — models with a 1M context
+window — but the status-line meter climbs ~5× faster than expected and pins at
+100%, auto-compaction fires early or not at all, and `/context` shows the limit
+as `… / 200k` instead of `/ 1M`.
+
+**Cause.** Claude Code only switches its context meter **and** auto-compaction to
+the 1M window (and sends the `context-1m` beta) when the session's model id
+carries the **`[1m]`** suffix (e.g. `claude-opus-4-8[1m]`). The selector and
+`config.json` advertise *bare* ids (`claude-opus-4-8`), so the client defaults to
+the 200k window even though Opus 4.8 / Opus 4.7 / Opus 4.6 / Sonnet 4.6 serve 1M
+natively on the Anthropic API. Nothing is actually lost upstream — the window is
+just mis-sized in the client.
+
+**Fix.** The launcher now appends `[1m]` automatically when the chosen
+orchestrator is a 1M-capable Claude model. Relaunch, pick the model, and confirm
+`/context` reads `/ 1M`.
+
+- **Disable it** (back to bare ids): set `UC_FORCE_1M=0`.
+- **Change the capable set:** set `UC_1M_MODELS` to a comma-separated list of base
+  ids (default `claude-opus-4-8,claude-opus-4-7,claude-opus-4-6,claude-sonnet-4-6`).
+- **Not affected:** Haiku 4.5 (200k only), `claude-auto`, and non-Claude routes
+  (Gemini / GPT / Composer) are never given a `[1m]` suffix.
+- **Caveat:** if your Anthropic-passthrough hop can fall back to a backend that
+  only supports 200k, a conversation that grows past 200k may then fail there —
+  make sure that fallback also honors 1M.
+
 ### Did I break my normal Claude Code?
 
 No — this project never edits your global `~/.claude` config or credentials; it
diff --git a/windows/Start-UltraCode.ps1 b/windows/Start-UltraCode.ps1
index ddddee9..a1d5a3a 100644
--- a/windows/Start-UltraCode.ps1
+++ b/windows/Start-UltraCode.ps1
@@ -84,9 +84,31 @@ $StateDir = Join-Path $env:LOCALAPPDATA "UltraCode-Shim"
 New-Item -ItemType Directory -Force -Path $StateDir | Out-Null
 $Settings = Join-Path $StateDir "ultracode_settings.json"
 $BaseUrl  = "http://127.0.0.1:$Port"
+
+# 1M context window enablement: Claude Code only switches its context meter AND
+# auto-compaction to the 1M window (and sends the context-1m beta) when the model
+# id carries the [1m] suffix. The selector/config advertise bare ids (e.g.
+# claude-opus-4-8), so without this the client sizes context at 200k -- the meter
+# fills ~5x too fast and pins at 100% -- even though Opus 4.8 / Sonnet 4.6 serve
+# 1M natively. We append [1m] to 1M-capable Claude base ids before launch.
+# Disable with UC_FORCE_1M=0; override the capable set with UC_1M_MODELS.
+function Add-Uc1m {
+    param([string]$ModelId)
+    if ($env:UC_FORCE_1M -eq "0") { return $ModelId }
+    if ([string]::IsNullOrEmpty($ModelId)) { return $ModelId }
+    if ($ModelId.Contains("[1m]")) { return $ModelId }
+    $set = if ($env:UC_1M_MODELS) { $env:UC_1M_MODELS }
+           else { "claude-opus-4-8,claude-opus-4-7,claude-opus-4-6,claude-sonnet-4-6" }
+    foreach ($id in $set.Split(",")) {
+        if ($ModelId -eq $id.Trim()) { return "${ModelId}[1m]" }
+    }
+    return $ModelId
+}
+$DefaultModel = Add-Uc1m "claude-opus-4-8"
+
 @{
     ultracode = $true
-    model     = "claude-opus-4-8"
+    model     = $DefaultModel
     env       = @{
         ANTHROPIC_BASE_URL                         = $BaseUrl
         CLAUDE_CODE_WORKFLOWS                       = "1"
@@ -231,6 +253,10 @@ if (($env:UC_SELECTOR -ne "0") -and (Test-Path $Selector)) {
         Write-Host "Selector unavailable; launching with default model: $_" -ForegroundColor Yellow
         $SelectedModel = ""
     }
+    # Upgrade a 1M-capable Claude pick to its [1m] variant so the client uses the
+    # full 1M context window (meter + auto-compaction), not the 200k default.
+    $SelectedModel = Add-Uc1m $SelectedModel
+    if ($SelectedModel) { Write-Host "Orchestrator model id: $SelectedModel" -ForegroundColor Green }
 }
 
 $HasModelArg = $false