feat(llma): add prompt management (#417)

* feat(llma): add prompt management

* chore(llma): bump version

* fix(llma): use SDK session with retry logic for prompt fetching

Use _get_session() from posthog/request.py instead of raw requests.get()
to benefit from the SDK's existing retry configuration on transient
network failures.

Author: Radu-Raicea

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 7.8.0 - 2026-01-28
+
+feat(llma): add prompt management
+
+Adds the Prompt Management feature. At the time of release, this feature is in a closed alpha.
+
 # 7.7.0 - 2026-01-15
 
 feat(ai): Add OpenAI Agents SDK integration

posthog/ai/__init__.py

@@ -0,0 +1,3 @@
+from posthog.ai.prompts import Prompts
+
+__all__ = ["Prompts"]

posthog/ai/prompts.py

@@ -0,0 +1,271 @@
+"""
+Prompt management for PostHog AI SDK.
+
+Fetch and compile LLM prompts from PostHog with caching and fallback support.
+"""
+
+import logging
+import re
+import time
+import urllib.parse
+from typing import Any, Dict, Optional, Union
+
+from posthog.request import DEFAULT_HOST, USER_AGENT, _get_session
+from posthog.utils import remove_trailing_slash
+
+log = logging.getLogger("posthog")
+
+DEFAULT_CACHE_TTL_SECONDS = 300  # 5 minutes
+
+PromptVariables = Dict[str, Union[str, int, float, bool]]
+
+
+class CachedPrompt:
+    """Cached prompt with metadata."""
+
+    def __init__(self, prompt: str, fetched_at: float):
+        self.prompt = prompt
+        self.fetched_at = fetched_at
+
+
+def _is_prompt_api_response(data: Any) -> bool:
+    """Check if the response is a valid prompt API response."""
+    return (
+        isinstance(data, dict)
+        and "prompt" in data
+        and isinstance(data.get("prompt"), str)
+    )
+
+
+class Prompts:
+    """
+    Fetch and compile LLM prompts from PostHog.
+
+    Can be initialized with a PostHog client or with direct options.
+
+    Examples:
+        ```python
+        from posthog import Posthog
+        from posthog.ai.prompts import Prompts
+
+        # With PostHog client
+        posthog = Posthog('phc_xxx', host='https://us.i.posthog.com', personal_api_key='phx_xxx')
+        prompts = Prompts(posthog)
+
+        # Or with direct options (no PostHog client needed)
+        prompts = Prompts(personal_api_key='phx_xxx', host='https://us.i.posthog.com')
+
+        # Fetch with caching and fallback
+        template = prompts.get('support-system-prompt', fallback='You are a helpful assistant.')
+
+        # Compile with variables
+        system_prompt = prompts.compile(template, {
+            'company': 'Acme Corp',
+            'tier': 'premium',
+        })
+        ```
+    """
+
+    def __init__(
+        self,
+        posthog: Optional[Any] = None,
+        *,
+        personal_api_key: Optional[str] = None,
+        host: Optional[str] = None,
+        default_cache_ttl_seconds: Optional[int] = None,
+    ):
+        """
+        Initialize Prompts.
+
+        Args:
+            posthog: PostHog client instance (optional if personal_api_key provided)
+            personal_api_key: Direct API key (optional if posthog provided)
+            host: PostHog host (defaults to US ingestion endpoint)
+            default_cache_ttl_seconds: Default cache TTL (defaults to 300)
+        """
+        self._default_cache_ttl_seconds = (
+            default_cache_ttl_seconds or DEFAULT_CACHE_TTL_SECONDS
+        )
+        self._cache: Dict[str, CachedPrompt] = {}
+
+        if posthog is not None:
+            self._personal_api_key = getattr(posthog, "personal_api_key", None) or ""
+            self._host = remove_trailing_slash(
+                getattr(posthog, "raw_host", None) or DEFAULT_HOST
+            )
+        else:
+            self._personal_api_key = personal_api_key or ""
+            self._host = remove_trailing_slash(host or DEFAULT_HOST)
+
+    def get(
+        self,
+        name: str,
+        *,
+        cache_ttl_seconds: Optional[int] = None,
+        fallback: Optional[str] = None,
+    ) -> str:
+        """
+        Fetch a prompt by name from the PostHog API.
+
+        Caching behavior:
+        1. If cache is fresh, return cached value
+        2. If fetch fails and cache exists (stale), return stale cache with warning
+        3. If fetch fails and fallback provided, return fallback with warning
+        4. If fetch fails with no cache/fallback, raise exception
+
+        Args:
+            name: The name of the prompt to fetch
+            cache_ttl_seconds: Cache TTL in seconds (defaults to instance default)
+            fallback: Fallback prompt to use if fetch fails and no cache available
+
+        Returns:
+            The prompt string
+
+        Raises:
+            Exception: If the prompt cannot be fetched and no fallback is available
+        """
+        ttl = (
+            cache_ttl_seconds
+            if cache_ttl_seconds is not None
+            else self._default_cache_ttl_seconds
+        )
+
+        # Check cache first
+        cached = self._cache.get(name)
+        now = time.time()
+
+        if cached is not None:
+            is_fresh = (now - cached.fetched_at) < ttl
+
+            if is_fresh:
+                return cached.prompt
+
+        # Try to fetch from API
+        try:
+            prompt = self._fetch_prompt_from_api(name)
+            fetched_at = time.time()
+
+            # Update cache
+            self._cache[name] = CachedPrompt(prompt=prompt, fetched_at=fetched_at)
+
+            return prompt
+
+        except Exception as error:
+            # Fallback order:
+            # 1. Return stale cache (with warning)
+            if cached is not None:
+                log.warning(
+                    '[PostHog Prompts] Failed to fetch prompt "%s", using stale cache: %s',
+                    name,
+                    error,
+                )
+                return cached.prompt
+
+            # 2. Return fallback (with warning)
+            if fallback is not None:
+                log.warning(
+                    '[PostHog Prompts] Failed to fetch prompt "%s", using fallback: %s',
+                    name,
+                    error,
+                )
+                return fallback
+
+            # 3. Raise error
+            raise
+
+    def compile(self, prompt: str, variables: PromptVariables) -> str:
+        """
+        Replace {{variableName}} placeholders with values.
+
+        Unmatched variables are left unchanged.
+        Supports variable names with hyphens and dots (e.g., user-id, company.name).
+
+        Args:
+            prompt: The prompt template string
+            variables: Object containing variable values
+
+        Returns:
+            The compiled prompt string
+        """
+
+        def replace_variable(match: re.Match) -> str:
+            variable_name = match.group(1)
+
+            if variable_name in variables:
+                return str(variables[variable_name])
+
+            return match.group(0)
+
+        return re.sub(r"\{\{([\w.-]+)\}\}", replace_variable, prompt)
+
+    def clear_cache(self, name: Optional[str] = None) -> None:
+        """
+        Clear cached prompts.
+
+        Args:
+            name: Specific prompt to clear. If None, clears all cached prompts.
+        """
+        if name is not None:
+            self._cache.pop(name, None)
+        else:
+            self._cache.clear()
+
+    def _fetch_prompt_from_api(self, name: str) -> str:
+        """
+        Fetch prompt from PostHog API.
+
+        Endpoint: {host}/api/projects/@current/llm_prompts/name/{encoded_name}/
+        Auth: Bearer {personal_api_key}
+
+        Args:
+            name: The name of the prompt to fetch
+
+        Returns:
+            The prompt string
+
+        Raises:
+            Exception: If the prompt cannot be fetched
+        """
+        if not self._personal_api_key:
+            raise Exception(
+                "[PostHog Prompts] personal_api_key is required to fetch prompts. "
+                "Please provide it when initializing the Prompts instance."
+            )
+
+        encoded_name = urllib.parse.quote(name, safe="")
+        url = f"{self._host}/api/projects/@current/llm_prompts/name/{encoded_name}/"
+
+        headers = {
+            "Authorization": f"Bearer {self._personal_api_key}",
+            "User-Agent": USER_AGENT,
+        }
+
+        response = _get_session().get(url, headers=headers, timeout=10)
+
+        if not response.ok:
+            if response.status_code == 404:
+                raise Exception(f'[PostHog Prompts] Prompt "{name}" not found')
+
+            if response.status_code == 403:
+                raise Exception(
+                    f'[PostHog Prompts] Access denied for prompt "{name}". '
+                    "Check that your personal_api_key has the correct permissions and the LLM prompts feature is enabled."
+                )
+
+            raise Exception(
+                f'[PostHog Prompts] Failed to fetch prompt "{name}": HTTP {response.status_code}'
+            )
+
+        try:
+            data = response.json()
+        except Exception:
+            raise Exception(
+                f'[PostHog Prompts] Invalid response format for prompt "{name}"'
+            )
+
+        if not _is_prompt_api_response(data):
+            raise Exception(
+                f'[PostHog Prompts] Invalid response format for prompt "{name}"'
+            )
+
+        return data["prompt"]