diff --git a/R/provider-gemini.R b/R/provider-gemini.R
index 293661e..b84a241 100644
--- a/R/provider-gemini.R
+++ b/R/provider-gemini.R
@@ -107,7 +107,7 @@ method(chat_request, ProviderGemini) <- function(provider,
     contents = contents,
     tools = tools,
     systemInstruction = system,
-    generation_config = generation_config,
+    generationConfig = generation_config,
     !!!extra_args
   ))
   req <- req_body_json(req, body)
@@ -131,7 +131,7 @@ method(stream_merge_chunks, ProviderGemini) <- function(provider, result, chunk)
   if (is.null(result)) {
     chunk
   } else {
-    merge_dicts(result, chunk)
+    merge_gemini_chunks(result, chunk)
   }
 }
 method(value_turn, ProviderGemini) <- function(provider, result, has_type = FALSE) {
@@ -158,6 +158,7 @@ method(value_turn, ProviderGemini) <- function(provider, result, has_type = FALS
       )
     }
   })
+  contents <- compact(contents)
   usage <- result$usageMetadata
   tokens <- c(
     usage$promptTokenCount %||% NA_integer_,
@@ -193,7 +194,13 @@ method(as_json, list(ProviderGemini, ToolDef)) <- function(provider, x) {
 }
 
 method(as_json, list(ProviderGemini, ContentText)) <- function(provider, x) {
-  list(text = x@text)
+  if (identical(x@text, "")) {
+    # Gemini tool call requests can include a Content with empty text,
+    # but it doesn't like it if you send this back
+    NULL
+  } else {
+    list(text = x@text)
+  }
 }
 
 # https://ai.google.dev/api/caching#FileData
@@ -249,3 +256,133 @@ method(as_json, list(ProviderGemini, TypeObject)) <- function(provider, x) {
     required = as.list(names2(x@properties)[required])
   ))
 }
+
+# Gemini-specific merge logic --------------------------------------------------
+
+merge_last <- function() {
+  function(left, right, path = NULL) {
+    right
+  }
+}
+
+merge_identical <- function() {
+  function(left, right, path = NULL) {
+    if (!identical(left, right)) {
+      stop("Expected identical values, but got ", deparse(left), " and ", deparse(right))
+    }
+    left
+  }
+}
+
+merge_any_or_empty <- function() {
+  function(left, right, path = NULL) {
+    if (!is.null(left) && nzchar(left)) {
+      left
+    } else if (!is.null(right) && nzchar(right)) {
+      right
+    } else {
+      ""
+    }
+  }
+}
+
+merge_optional <- function(merge_func) {
+  function(left, right, path = NULL) {
+    if (is.null(left) && is.null(right)) {
+      NULL
+    } else {
+      merge_func(left, right, path)
+    }
+  }
+}
+
+merge_objects <- function(...) {
+  spec <- list(...)
+  function(left, right, path = NULL) {
+    # cat(paste(collapse = "", path), "\n")
+    stopifnot(is.list(left), is.list(right), all(nzchar(names(spec))))
+    mapply(names(spec), spec, FUN = function(key, value) {
+      value(left[[key]], right[[key]], c(path, ".", key))
+    }, USE.NAMES = TRUE, SIMPLIFY = FALSE)
+  }
+}
+
+merge_candidate_lists <- function(...) {
+  merge_unindexed <- merge_objects(...)
+  merge_indexed <- merge_objects(index = merge_identical(), ...)
+
+  function(left, right, path = NULL) {
+    if (length(left) == 1 && length(right) == 1) {
+      list(merge_unindexed(left[[1]], right[[1]], c(path, "[]")))
+    } else {
+      # left and right are lists of objects with [["index"]]
+      # We need to find the elements that have matching indices and merge them
+      left_indices <- vapply(left, `[[`, integer(1), "index")
+      right_indices <- vapply(right, `[[`, integer(1), "index")
+      # I know this seems weird, but according to Google's Go SDK, we should
+      # only retain indices on the right that *already* appear on the left.
+      # Citations:
+      # https://github.com/google/generative-ai-go/blob/3d14f4039eaef321b15bcbf70839389d7f000233/genai/client_test.go#L655
+      # https://github.com/google/generative-ai-go/blob/3d14f4039eaef321b15bcbf70839389d7f000233/genai/client.go#L396
+      lapply(left_indices, function(index) {
+        left_item <- left[[which(left_indices == index)]]
+        right_item <- right[[which(right_indices == index)]]
+        if (is.null(right_item)) {
+          left_item
+        } else {
+          merge_indexed(left_item, right_item, c(path, "[", index, "]"))
+        }
+      })
+    }
+  }
+}
+
+merge_append <- function() {
+  function(left, right, path = NULL) {
+    c(left, right)
+  }
+}
+
+merge_parts <- function() {
+  function(left, right, path = NULL) {
+    joined <- c(left, right)
+
+    # Identify text parts
+    is_text <- map_lgl(joined, ~is.list(.x) && identical(names(.x), "text"))
+
+    # Create groups for contiguous sections
+    groups <- cumsum(c(TRUE, diff(is_text) != 0))
+
+    # Split into groups and process each
+    split_parts <- split(joined, groups)
+    merged_split_parts <- map2(split_parts, split(is_text, groups), function(parts, is_text_group) {
+      if (!is_text_group[[1]]) {
+        # Non-text group: return parts unchanged
+        return(parts)
+      } else {
+        # Text group: merge text values
+        text_values <- map_chr(parts, ~.x[["text"]])
+        list(list(text = paste0(text_values, collapse = "")))
+      }
+    })
+    unlist(merged_split_parts, recursive = FALSE, use.names = FALSE)
+  }
+}
+
+# Put it all together...
+merge_gemini_chunks <- merge_objects(
+  candidates = merge_candidate_lists(
+    content = merge_objects(
+      role = merge_any_or_empty(),
+      parts = merge_parts()
+    ),
+    finishReason = merge_last(),
+    safetyRatings = merge_last(),
+    citationMetadata = merge_optional(
+      merge_objects(citationSources = merge_append())
+    ),
+    tokenCount = merge_last()
+  ),
+  promptFeedback = merge_last(),
+  usageMetadata = merge_last()
+)
diff --git a/R/utils.R b/R/utils.R
index a612087..d497733 100644
--- a/R/utils.R
+++ b/R/utils.R
@@ -47,6 +47,7 @@ last_response_json <- function() {
 }
 print_json <- function(x) {
   cat(pretty_json(x))
+  cat("\n")
 }
 pretty_json <- function(x) {
   jsonlite::toJSON(x, pretty = TRUE, auto_unbox = TRUE)
diff --git a/tests/testthat/helper-provider.R b/tests/testthat/helper-provider.R
index b0dde20..55edd43 100644
--- a/tests/testthat/helper-provider.R
+++ b/tests/testthat/helper-provider.R
@@ -52,7 +52,10 @@ test_tools_simple <- function(chat_fun) {
   chat <- chat_fun(system_prompt = "Be very terse, not even punctuation.")
   chat$register_tool(tool(function() "2024-01-01", "Return the current date"))
 
-  result <- chat$chat("What's the current date in YMD format?", echo = TRUE)
+  expect_output(
+    result <- chat$chat("What's the current date in YMD format?", echo = TRUE),
+    "2024-01-01"
+  )
   expect_match(result, "2024-01-01")
 
   result <- chat$chat("What month is it? Provide the full name")
@@ -114,7 +117,7 @@ test_tools_sequential <- function(chat_fun, total_calls) {
 
 test_data_extraction <- function(chat_fun) {
   article_summary <- type_object(
-    "Summary of the article.",
+    "Summary of the article. Preserve existing case.",
     title = type_string("Content title"),
     author = type_string("Name of the author")
   )
diff --git a/tests/testthat/test-provider-gemini.R b/tests/testthat/test-provider-gemini.R
index a2546de..90d675d 100644
--- a/tests/testthat/test-provider-gemini.R
+++ b/tests/testthat/test-provider-gemini.R
@@ -48,3 +48,26 @@ test_that("can use images", {
   test_images_inline(chat_fun)
   test_images_remote_error(chat_fun)
 })
+
+# chunk merging ----------------------------------------------------------
+
+test_that("can merge text output", {
+  # output from "tell me a joke" with text changed
+  messages <- c(
+    '{"candidates": [{"content": {"parts": [{"text": "a"}],"role": "model"}}],"usageMetadata": {"promptTokenCount": 5,"totalTokenCount": 5},"modelVersion": "gemini-1.5-flash"}',
+    '{"candidates": [{"content": {"parts": [{"text": "b"}],"role": "model"}}],"usageMetadata": {"promptTokenCount": 5,"totalTokenCount": 5},"modelVersion": "gemini-1.5-flash"}',
+    '{"candidates": [{"content": {"parts": [{"text": "c"}],"role": "model"},"finishReason": "STOP"}],"usageMetadata": {"promptTokenCount": 5,"candidatesTokenCount": 17,"totalTokenCount": 22},"modelVersion": "gemini-1.5-flash"}'
+  )
+  chunks <- lapply(messages, jsonlite::parse_json)
+
+  out <- merge_gemini_chunks(chunks[[1]], chunks[[2]])
+  out <- merge_gemini_chunks(out, chunks[[3]])
+
+  expect_equal(out$candidates[[1]]$content$parts[[1]]$text, "abc")
+  expect_equal(out$usageMetadata, list(
+    promptTokenCount = 5,
+    candidatesTokenCount = 17,
+    totalTokenCount = 22
+  ))
+  expect_equal(out$candidates[[1]]$finishReason, "STOP")
+})