diff --git a/shortfin/python/shortfin_apps/llm/components/kvcache/base_attention_cache.py b/shortfin/python/shortfin_apps/llm/components/kvcache/base_attention_cache.py
index 4dde584a8..b2dc4a7e3 100644
--- a/shortfin/python/shortfin_apps/llm/components/kvcache/base_attention_cache.py
+++ b/shortfin/python/shortfin_apps/llm/components/kvcache/base_attention_cache.py
@@ -38,17 +38,21 @@ def __init__(self, page_pool, tokens_per_page):
         self.tokens_per_page = tokens_per_page
     
 
-    def acquire_pages_for_tokens(self, tokens: List[int]) -> tuple[List[PageInfo], int)]:
+    def acquire_pages_for_tokens(self, tokens: List[int], extra_token_slots: int = 1) -> tuple[List[PageInfo], int)]:
         """
         Given a list of tokens, return a list of pages and a start position to continue generation from.
 
+        Parameters:
+        - tokens: all the known tokens for this generation request
+        - extra_token_slots: number of kvcache slots needed in addition to the ones needed to hold the given tokens. 
+
         In the base implementation, this will just allocate all new pages, but in shared-kv implementations, we will fetch cached pages if applicable.
 
         The pages are returned in order.
 
         No token at idx < n_cached_token should be written to. TODO: consider enforcing this.
         """
-        pages_needed = math.ceil(len(tokens) / self.tokens_per_page)
+        pages_needed = math.ceil(len(tokens + extra_token_slots) / self.tokens_per_page)
         pages = self.page_pool.acquire_free_pages(pages_needed)
 
         n_cached_tokens = 0
diff --git a/shortfin/python/shortfin_apps/llm/components/service.py b/shortfin/python/shortfin_apps/llm/components/service.py
index bcd08b756..6fa44fbf9 100644
--- a/shortfin/python/shortfin_apps/llm/components/service.py
+++ b/shortfin/python/shortfin_apps/llm/components/service.py
@@ -218,7 +218,11 @@ def board_prefills(self, cache: AttnPageCache):
             needed_pages = math.ceil(
                 len(prefill_request.input_token_ids) / self.page_seq_stride
             )
-            pages = cache.acquire_free_pages(needed_pages)
+            # allocate kv cache pages
+            pages, cache_hit_prefix_length = cache.acquire_pages_for_tokens(
+                prefill_request.input_token_ids,
+                extra_token_slots=0, # prefill needs no extra kvcache slots to write to
+            )
             if pages is None:
                 logger.debug("Cannot fulfill request for %d pages", needed_pages)
                 continue
@@ -254,7 +258,11 @@ def board_decodes(self, cache: AttnPageCache):
                 / self.page_seq_stride
             )
             if needed_pages > len(decode_request.locked_pages):
-                pages = cache.acquire_free_pages(needed_pages)
+                # allocate kv cache pages
+                pages, cache_hit_prefix_length = cache.acquire_pages_for_tokens(
+                    decode_request.input_token_ids,
+                    extra_token_slots=1, # need 1 extra slot to write result.
+                )
                 if pages is None:
                     logger.debug(
                         "Cannot fulfill decode request for %d pages", needed_pages